Intrauterine growth retardation (IUGR) is a major cause of perinatal mortality and morbidity which may be amenable to prevention and intervention. However, approximately 40% of IUGR has no obvious cause. To create a strategic basis for prevention, more efforts are warranted to identify risk factors for idiopathic IUGR. This study aims to identify risk factors/predictors for idiopathic IUGR and subtypes (symmetric and asymmetric) with special focus on chlamydia infection and maternal serum alpha-fetoprotein. In addition, this study will go beyond the conventional definitions of birth-weight-for-gestational-age referenced IUGR (the 10th percentile) and symmetry of fetal growth (Ponderal index), and it will explore better race-specific definitions of symmetric and asymmetric IUGR, incorporating clinical and anthropometric measurements. Racial differences in incidence rates, patterns of IUGR, and neonatal mortality and morbidity will be compared and race-specific risk factors investigated. Data for this project are derived from the obstetric and neonatal databases in the Department of Obstetrics, Gynecology and Reproductive Sciences, and the Department of Pediatrics in the Mount Sinai Medical Center in New York, with approximately 40,000 ethnically and socioeconomically diverse pregnancies and over 1000 variables for each mother-neonate pair. The specific aims of the study are as follow. (1) Define IUGR and symmetry of fetal growth incorporating birth weight, crown-heel length, head circumference, gestational age, and perinatal mortality. (2) Compare the distribution and incidence rates of symmetric and asymmetric IUGR in Asians, blacks, Hispanics and whites. (3) Examine the neonatal morbidity and mortality in relation to symmetric and asymmetric IUGR, and the racial differences. (4) Identify risk factors/predictors for idiopathic symmetry and asymmetry IUGR in different ethnic groups. (5) Examine the associations between chlamydia infection during pregnancy and idiopathic IUGR, and between maternal serum alpha-fetoprotein and idiopathic IUGR. (6) Finally, compare the results based on the new definitions of IUGR and symmetry with those based on 10th percentile and ponderal index.